A common objective of threaded fasteners is to be tightened to a sufficient but not excessive torque and then to be locked so as to retain that torque setting and the associated axial tensile preload on a shank member such as a bolt to which the threaded fastener is tightened. There are numerous examples in the art of such devices one of which is the well-known fastener shown in George S. Wing U.S. Pat. No. 2,940,495, issued June 14, 1960.
The fastener of the Wing patent utilizes a collar which includes a nut section that is internally threaded and is to be tightened onto a threaded shank. Integral with the nut section is a drive section with driver-engaging surfaces connected to the nut section by a shear section which has the least torque resistance of the three sections. When the predetermined torque is applied to the drive section the shear section fractures, and the drive section falls free, leaving the nut section correctly tightened onto the shank. In this classical fastener, a thread lock is exerted by a portion of the nut section having been initially pressed out of round and which is rounded out by engagement with the external thread so that the resulting springback exerts the desired locking action.
There has recently been developed a device known as "Eddie Bolt", in which a nut is formed with a set of external ribs that are engaged by a driver in such a way that the ribs are deflected radially inwardly and are plastically deformed as the consequence of application of a suitable torque on the ribs. The inward displacement of material of these ribs causes inward displacement of the nut material to engage the thread of a shank thereby to exert a locking force. The external rib is relied on both for torque definition and also for a locking action. This leads to an unfortunately critical relationship between the two functions.
It is an object of this invention to provide a fastener which can be locked to a thread having a non-circular convolution by inward displacement of rib and nut section material, but only after the nut has been set to a predetermined torque, and without thereafter affecting the torque setting.